a) Field of the Invention
The present invention relates to a system for producing full color enlargements of color transparencies or negatives on photographic papers.
The invention also relates to a method for producing full color enlargements of color transparencies or negatives on photographic papers which method makes use of the inventive system.
b) Brief Description of the Prior Art
In the photographic art, a conventional method that is commonly used for producing a full color enlargement of a color transparency or negative on a photographic paper, consists in projecting the color transparency or negative onto the photographic paper in such a manner as directly to obtain the requested "blow up". Another conventional method consists in producing an enlarged negative from the transparency or negative on a photographic film and then using the enlarged negative to print the requested enlargement on a photographic paper, by contact or any other technique well known in this particular field. A further conventional method consists in producing color separation negatives of the transparency or negative on a photographic film, blowing up these color separation negatives, and then using them in a tri-color printing system known per se, to produce the requested enlargement onto a photographic paper.
In all of these conventional methods used to produce photographic enlargements, it is compulsory that the contrast of the transparency or negative to be enlarged and, of course, of any enlarged negative or separation negative produced along the method, be adjusted to match with the characteristics of the photographic paper being used, which are commonly "adapted" for contrasts ranging from 20 to 110.
In the following specification, the word "contrast" is defined as the difference between the maximum and minimum densities. A definition of the term "density" as used in photography is given in the pamphlet "PRACTICAL DENSITOMETRY" printed by Eastman Kodak Company of Rochester, N.Y. At page 23 of this brochure, it is indicated that density normally ranges from 0 to 3.0. However, for ease of manipulation of the density numbers, these numbers are multiplied by 100 (0 to 300). This is the convention which is adapted in the present specification.
In another technical field, namely the graphic arts, a conventional method that is commonly used for printing full color enlargements of a color transparency or negative, consists in producing enlarged color separation negatives of the transparency or negative with a laser scanner and then using these separation negatives to produce printing plates that can subsequently be used in a rotographic or offset printing machine (see U.S. Pat. Nos. 4,325,631 and 4,647,182).
In this particular case, it is essential that a maximum of contrast be obtained when the color separation negatives are produced, since these negatives have to be highly contrasted (up to 290) in order to subsequently produce the printing plates or screened substrates that are used in the printing machine.
All the laser scanners that are presently used in this particular industry, are designed to produce "screened negatives" consisting of myriads of solid dots on a transparent base. As a matter of fact, dots have become the conventional method of producing separation negatives for use in printing industry.
Another type of scanner, known as "continuous tone scanner", has also been used in the past for the same purpose, namely to produce separation negatives for use in the printing industry. Such a continuous tone scanner makes use of a special photographic film hereinafter called "continuous tone photographic film", and produces negatives which are made up of hundreds of thousands of ultra-fine lines extending parallel to each other all over the film, in a number of 100 to 300 per centimeter. An example of continuous tone laser scanner including a color correction computer, is disclosed by way of example in U.S. Pat. No. 3,622,690.
Once again, the continuous tone scanner to be efficient in the printing industry, must produce highly contrasted separation negatives. Thus, such a scanner also works with contrast up to 290.
This kind of continuous tone scanner is now considered as obsolete because it produces negatives that have to be screened in order to be used in a printing machine. Therefore, it is no more in use.